First Time Royal Caribbean cruisers.

My wife and I are on The Voyager of the Seas from Singapore to Sydney . Through Indonesian islands to Darwin then around Cape York down to Sydney.
What sort of formal or semi formal clothes should we pack. I no longer have a tux but a dark suit - is this suitable? We will have spent time at Marriott ****et Beach resort prior where we will be shorts, T shirt and sandals attired. Much of that will be OK for casual onboard but just uncertain about the more 'formal' aspects on board. Thanks in advance - we are newly retired at 70.